This invention relates generally to nanoscale molecular assemblies and, more specifically, to the use of structural subunits called xe2x80x9csynthonsxe2x80x9d in the design and manufacture of molecular macrostructures, machines, and devices.
The invention relates to molecular assemblies at the nanoscale, commonly referred to as nanosystems, and, more specifically, to macromolecular nanostructures and advanced materials using a design motif based on the application of main group and transition metal polyhedral clusters as rigid components in the design of structural subunits for the construction of nanoscale molecular assemblies.
Recent years have witnessed truly remarkable achievements in many fields of science and technology. Among these, advances in the areas of new materials and macromolecules with designed features have been particularly dramatic. Theoreticians are now seriously proposing the cognizant design and unidirectional fabrication of atomic and molecular assemblies on the nanometer scale with atomic precision (1). The design and construction of large-scale molecular arrays is clearly the enabling science for the realization of the proposed potential of nanotechnology. While it is expected that the realization of this potential may be far in the future, the proposed structures and molecular assemblies are currently serving as goals for both theoretical and experimental studies. Along the way, many of the smaller molecules and assemblies intermediate in the fabrication of these and other proposed larger structures are fully expected, in their own right, to provide immediate and significant advances in a variety of areas, including macromolecular design and construction, optoelectronic applications, medicine, and new advanced materials.
Chemists have long been involved with the design and synthesis of functionalized molecules with specific structural, chemical, and physical properties. Few of these studies, however, have focused on the use of molecular functionalization as a means to the directional design of structural building elements for the fabrication of larger mechanical and rigid structures at the nanoscale. Studies toward this focus have recently been pursued by the consideration of large atomic assemblies for a variety of both chemical and mechanical applications. Various terms, including nanosystems and nanoscale materials, have been used to describe this emerging field.
Most of the work thus far in nanoscale design has employed carbon as the primary structural element. Diamondoid structures, diamond thin films, and aromatic hydrocarbons (buckminsterfullerenes or, more commonly, xe2x80x9cbuckyxe2x80x9d species) are receiving a great deal of attention due to their chemical and physical properties and, in the case of xe2x80x9cbuckyxe2x80x9d systems, the ease of synthesis (though this ease does not currently correlate well with either the control or specificity of xe2x80x9cbuckyxe2x80x9d synthesis). In stark contrast, boron-based materials, and main group and transition metal polyhedral cluster species in general, have been comparatively neglected as potential alternatives to these organic materials, which, in many ways, have received significant attention because of the familiarity of carbon and organic molecules in general to current nanoscale theorists actively designing macromolecules and nanosystems. Of special interest are the polyhedral boron cluster systems, one of the primary topics of this document, due to their unique chemical, physical, and synthetic properties.
For a very long time, philosophers and scientists have been fascinated by the intrinsic beauty and three dimensional shapes of polyhedra (many-faced solids). Since the work of Plato and Archimedes, philosophers, mathematicians, and, most recently, physical scientists have focused their attention on these intriguing polyhedral bodies. It is the field of main group cluster chemistry that most closely ties together the abstract, mathematical study of these pure polyhedra with the real physical and chemical world. In particular, main group cluster chemistry may be thought of as the xe2x80x9cmissing linkxe2x80x9d between small molecule behavior, with more localized bonding, and that of extended arrays and macromolecular assemblies, with extensively delocalized electronic structures. It is believed that the design and fabrication of many of the new three dimensional nanoscale molecular architectures currently being proposed and developed in the pursuit of viable molecule-based nanosystem construction may best be accomplished, in part, through the use of these polyhedral and related building blocks.
Main group clusters have presented considerable challenges to synthetic, structural, and theoretical chemists since their discovery nearly ninety years ago. The quest for a detailed understanding of these polyhedral species has led to an understanding of some very remarkable chemistry. Boron-based polyhedral structures display a number of unique chemical, physical, and structural properties that may make them particularly suitable for the fabrication of complex molecular architectures. When viewed from either a nanoscale macrostructural or materials perspective, these polyhedral cluster compounds and assemblies provide extraordinary structures with an anticipated array of unique properties, such as high stabilities, high degrees of systemic interconnection through the potential for extensive three-dimensional bonding, and high-strength molecular architectures.
With the remarkable geometric and bonding properties of these cluster species comes the flexibility of either treating each main group or transition metal cluster as a design unit in its own right or using each cluster as part of some larger synthetic subunit for the design of larger systems based on the construction limitations imposed by the new, larger subunit. The route proposed here for the construction of these remarkable structures and compounds is via the design and synthesis of smaller, structurally simple synthon elements for the subsequent design of larger macromolecular assemblies. These structures, along with proposed synthetic pathways and potential short-term applications, are described in the following sections of this document.